1. Field of the Invention
The present invention relates to an image-shake correcting device for preventing an image picked up by an image pickup apparatus from being shaken by a vibration of a hand or the like and, more particularly, to an image-shake correcting device suitable for use in an image pickup apparatus, such as a portable video camera.
2. Description of the Related Art
It is known that, in an image pickup apparatus such as a video camera, whether the industrial or domestic type, a vibration of the camera visually impairs an image and causes various kinds of malfunctions. It is also known that an image shake easily occurs particularly when photography is performed during walking, in a vehicle which is running, or in a place which vibrates to a significant extent. For these reasons, to correct such an image shake, it has heretofore been proposed to provide various types of image-shake correcting devices which will be described below.
For example, an inertial pendulum type of image-shake correcting device (U.S. Pat. Nos. 2,959,088 and 2,829,557 and the like) is known. In the inertial pendulum type of image-shake preventing device, an inertial pendulum type of shake preventing lens having a two-axes gimbal structure is disposed around a master lens, and an image shake is cancelled by this shake preventing lens, thereby correcting the image shake. Another example is a variable-angle-prism type of image-shake correcting device in which a variable angle prism for varying the optical axis of a lens (front lens) is disposed in front of the lens, and which is arranged to detect a movement from an image signal outputted from an image pickup element (CCD) or to detect a movement by means of an acceleration sensor, and drive the variable angle prism on the basis of the resultant detection signal, thereby correcting an image shake. Yet another example is a purely electronic image-shake correcting device which is arranged to store a video signal outputted from an image pickup element (CCD) in an image memory or the like, detect an image shake from information about the video signal to find the amount of displacement of the image, and shift an image reading address of the image memory according to the amount of displacement of the image, thereby correcting the image shake (Japanese Laid-Open Patent Application No. Sho 63-166370).
The third one of the above-described examples, i.e., the purely electronic image-shake correcting device, has recently received attention. This is because the purely electronic image-shake correcting device does not need any special mechanical mechanism for correcting an image shake and can be reduced in size, weight and cost owing to the rapid advance of semiconductor technology which makes it possible to accommodate a large-scale electrical circuit into an extremely small package.
However, the above-described purely electronic image-shake correcting device has a number of problems. For example, if an electronically enlarged image is corrected by moving (shifting) the electronically enlarged image with a correction step of not greater than the minimum pixel of the image pickup element, a moirxc3xa9 noise which leads to an image degradation may be caused by a movement of a position at which a resolution degradation occurs due to image enlargement processing, although the degree of the moirxc3xa9 noise depends on an image enlargement ratio and the kind of image. If an image is not electronically enlarged and is merely moved with the correction step of not greater than the minimum pixel of the image pickup element, a resolution degradation still occurs and a large image degradation occurs due to image-shake correction.
A first object of the present invention which has been made in light of the above-described problems is to provide an electronic image-shake correcting device which causes no large image degradation.
A second object of the present invention is to provide an image-shake correcting device capable of minimizing a resolution degradation and a moirxc3xa9 noise due to a movement of the position of occurrence of the resolution degradation, thereby minimizing an image degradation due to image-shake correction.
To achieve the above-described objects, according to one aspect of the present invention, there is provided an image pickup apparatus which comprises motion-vector detecting means for detecting a motion vector relative to images, electronic correcting means for electronically correcting an image shake on the basis of the motion vector detected by the motion-vector detecting means, image enlarging means for performing image enlargement processing on a picked-up image signal whose image shake is corrected by the electronic correcting means, image-enlargement-ratio varying means for varying an image enlargement ratio of the image enlarging means, and control means for controlling a correction step of the electronic correcting means in accordance with the image enlargement ratio set by the image-enlargement-ratio varying means to set the correction step to an optimum state.
To achieve the above-described objects, according to another aspect of the present invention, there is provided an image pickup apparatus which comprises image pickup means, motion-vector detecting means for detecting a motion vector relative to images, absolute-deviation computing means for computing an absolute deviation from a reference point of a current image on the basis of the motion vector detected by the motion-vector detecting means, electronic correcting means for electronically correcting an image shake on the basis of the absolute deviation computed by the absolute-deviation computing means, detecting means for detecting whether the image pickup means is fixed, and control means for controlling a correction step of the electronic correcting means on the basis of a detection signal provided by the detecting means to set the correction step to an optimum state.
To achieve the above-described objects, according to yet another aspect of the present invention, there is provided an image pickup apparatus which comprises motion-vector detecting means for detecting a motion vector relative to images, absolute-deviation computing means for computing an absolute deviation from a reference point of a current image on the basis of the motion vector detected by the motion-vector detecting means, electronic correcting means for electronically correcting an image shake on the basis of the absolute deviation computed by the absolute-deviation computing means, zoom magnification detecting means for detecting a zoom magnification, and control means for controlling a correction step of the electronic correcting means according to the zoom magnification detected by the zoom magnification detecting means to set the correction step to an optimum state.
The above and other objects, features and advantages of the present invention will become apparent from the following detailed description of preferred embodiments of the present invention, taken in conjunction with the accompanying drawings.